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fix(eslint-plugin): [no-unnecessary-type-parameters] check mapped alias type arguments #9741

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Merged
merged 4 commits into from
Aug 20, 2024
Merged

fix(eslint-plugin): [no-unnecessary-type-parameters] check mapped alias type arguments #9741

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4289adb
fix(eslint-plugin): [no-unnecessary-type-parameters] check mapped ali…
JoshuaKGoldberg Aug 6, 2024
c1dfdc6
Merge branch 'main' into no-unnecessary-type-parameters-check-alias-t…
JoshuaKGoldberg Aug 12, 2024
469e933
yarn format --write
JoshuaKGoldberg Aug 12, 2024
cc6563c
Handle type aliases higher up in #9741 (#323)
danvk Aug 19, 2024
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16 changes: 7 additions & 9 deletions packages/eslint-plugin/src/rules/no-unnecessary-type-parameters.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -258,6 +258,13 @@ function collectTypeParameterUsageCounts(
}
}

// Catch-all: generic type references like `Exclude<T, null>`
else if (type.aliasTypeArguments) {
// We don't descend into the definition of the type alias, so we don't
// know whether it's used multiple times. It's safest to assume it is.
visitTypesList(type.aliasTypeArguments, true);
}

// Intersections and unions like `0 | 1`
else if (tsutils.isUnionOrIntersectionType(type)) {
visitTypesList(type.types, assumeMultipleUses);
Expand Down Expand Up @@ -307,10 +314,6 @@ function collectTypeParameterUsageCounts(
}
}

for (const typeArgument of type.aliasTypeArguments ?? []) {
visitType(typeArgument, true);
}

visitType(type.getNumberIndexType(), true);
visitType(type.getStringIndexType(), true);

Expand All @@ -329,11 +332,6 @@ function collectTypeParameterUsageCounts(
else if (isOperatorType(type)) {
visitType(type.type, assumeMultipleUses);
}

// Catch-all: generic type references like `Exclude<T, null>`
else if (type.aliasTypeArguments) {
visitTypesList(type.aliasTypeArguments, true);
}
}

function incrementIdentifierCount(
Expand Down
18 changes: 18 additions & 0 deletions packages/eslint-plugin/tests/rules/no-unnecessary-type-parameters.test.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -342,6 +342,24 @@ ruleTester.run('no-unnecessary-type-parameters', rule, {
(token): token is Exclude<TSESTree.Token, Conditions & ExtractedToken> =>
tokenType in conditions;
`,
`
type Foo<T, S> = S extends 'somebody'
? T extends 'once'
? 'told'
: 'me'
: never;

declare function foo<T>(data: T): <S>(other: S) => Foo<T, S>;
`,
`
type Foo<T, S> = S extends 'somebody'
? T extends 'once'
? 'told'
: 'me'
: never;

declare function foo<T>(data: T): <S>(other: S) => Foo<S, T>;
`,
`
declare function mapObj<K extends string, V>(
obj: { [key in K]?: V },
Expand Down
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